Separation of alpha emitting species from plating baths

ABSTRACT

A non alpha controlled plating bath including Tin species and a trace amount of Polonium species is utilized in a plating tool. The plating tool includes a Polonium filter element to remove Polonium species from the plating bath to selectively plate Tin upon a plating cathode. The filter may include a Titanium inner portion surrounding by a stannic oxide exterior. The filter may reduce the Polonium species by having the polonium absorb and then enter within the stannic oxide matrix. The filter may be located within the plating tool reservoir or filter housing. The filter may be fabricated by forming Tin upon a Titanium backbone and converting the Tin to stannic oxide.

FIELD

Embodiments of invention generally relate to the fabrication ofsemiconductor devices, such as a wafer, semiconductor chip, chipcarrier, etc. More particularly, embodiments relate to removing alphaparticle emitting species, such as Polonium (Po), from a plating bathutilized in the fabrication of conductive elements, such as contacts, insemiconductor devices.

BACKGROUND

Formation of integrated circuit structures of a semiconductor device mayutilize plating processes. During plating, a metal or other electricallyconductive material is plated from an exposed surface. In certainimplementations the electrically conductive material takes the form ofcontacts, solder bumps, etc. that are utilized to interconnect thesemiconductor device to external circuitry.

The Restriction of Hazardous Substances Directive (RoHS) restricts theuse of certain hazardous substances in electrical and electronicequipment and has driven the electronics industry to move away fromsolders that contain Lead (Pb). As a result, lead-free solder material,such as Tin (Sn), may now be utilized in the solder bump platingprocesses.

In order to reduce soft errors within the semiconductor device it may bebeneficial to utilize low alpha particle emitting electricallyconductive materials in the plated electrically conductive materials. Alow alpha particle emitting electrically conductive material is anelectrically conductive material having an alpha particle emissivityvalue of less than 2α/cm²/1000 hours. However, the cost of low alphaparticle emitting electrically conductive materials may be 2-7 times thecost of the associated raw material which may include a trace amount ofalpha particle emitting particles.

SUMMARY

In an embodiment of the present invention, a method of fabricating afilter comprising a Polonium (Po) filter element that filters Poincludes forming Tin (Sn) upon a Titanium (Ti) interior and convertingthe Sn to stannic oxide.

This and other embodiments, features, aspects, and advantages willbecome better understood with reference to the following description,appended claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention are attained and can be understood in detail, a moreparticular description of the invention, briefly summarized above, maybe had by reference to the embodiments thereof which are illustrated inthe appended drawings.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 depicts a semiconductor wafer that may include variousembodiments of the present invention.

FIG. 2 depicts a cross section view of a semiconductor device that mayinclude various embodiments of the present invention.

FIG. 3 depicts a cross section view of a semiconductor carrier that mayinclude various embodiments of the present invention.

FIG. 4 depicts a cross section view of a semiconductor device at aparticular stage of fabrication, according to embodiments of the presentinvention.

FIG. 5 and FIG. 6 depict respective plating tools and semiconductordevices at a particular stage of fabrication, in accordance with variousembodiments of the present invention.

FIG. 7 and FIG. 8 depict cross sections of a semiconductor device atparticular stages of fabrication, according to embodiments of thepresent invention.

FIG. 9 depicts electrochemistry Sn and Po plating curves.

FIG. 10 depicts a semiconductor device fabrication method to formelectrically conductive material thereupon by selectively plating Snwhile suppressing plating of Po, according to embodiments of the presentinvention.

FIG. 11 depicts a plating tool and semiconductor device at a particularstage of fabrication, in accordance with various embodiments of thepresent invention.

FIG. 12 depicts a semiconductor device fabrication method to formelectrically conductive material thereupon by selectively plating Snwhile suppressing plating of Po, according to embodiments of the presentinvention.

FIG. 13 and FIG. 14 depict respective plating tools and semiconductordevices at a particular stage of fabrication, in accordance with variousembodiments of the present invention.

FIG. 15, FIG. 16A, and FIG. 16B depict respective tanks utilized toseparate Po from a Sn alloy including Sn and a trace amount of Po,herein after referred to as a SnPo alloy, according to embodiments ofthe present invention.

FIG. 17A, FIG. 17B, and FIG. 17C depict methods to separate Po from aSnPo alloy, according to embodiments of the present invention.

FIG. 18 depicts a SnPo alloy, according to embodiments of the presentinvention.

FIG. 19A depicts a SnPo alloy Sn oxidation and Po accumulationtechnique, according to embodiments of the present invention.

FIG. 19B depicts a SnPo alloy Sn oxidation and Po accumulation techniqueperformed upon a semiconductor device, according to embodiments of thepresent invention.

FIG. 19C depicts a SnPo alloy Sn oxidation and Po accumulation techniqueperformed upon a semiconductor carrier, according to embodiments of thepresent invention.

FIG. 20 depicts a purified Sn alloy including Sn and reduced Po,according to embodiments of the present invention.

FIG. 21 depicts a method of forming a purified Sn alloy including Sn andreduced Po, according to embodiments of the present invention.

FIG. 22 depicts a method of forming a purified Sn alloy solder bump,including Sn and reduced Po, upon a semiconductor device orsemiconductor carrier, according to embodiments of the presentinvention.

FIG. 23 depicts a plating tool and semiconductor device at a particularstage of fabrication, in accordance with various embodiments of thepresent invention.

FIG. 24 depicts a filter element utilized in a plating tool, inaccordance with various embodiments of the present invention.

FIG. 25 depicts a method of forming a filter element, in accordance withvarious embodiments of the present invention.

FIG. 26 depicts a method of filtering Po from a plating bath, inaccordance with various embodiments of the present invention.

FIG. 27 depicts a plating tool and semiconductor device at a particularstage of fabrication, in accordance with various embodiments of thepresent invention.

The drawings are not necessarily to scale. The drawings are merelyschematic representations, not intended to portray specific parametersof the invention. The drawings are intended to depict only exemplaryembodiments of the invention. In the drawings, like numbering representslike elements.

DETAILED DESCRIPTION

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it can be understood that the disclosed embodiments aremerely illustrative of the claimed structures and methods that may beembodied in various forms. These exemplary embodiments are provided sothat this disclosure will be thorough and complete and will fully conveythe scope of this invention to those skilled in the art. In thedescription, details of well-known features and techniques may beomitted to avoid unnecessarily obscuring the presented embodiments.

Various embodiments are related to non alpha particle controlled Tinincluding Tin and a trace amount of Polonium being utilized as a platinganode to selectively plate Tin upon a plating cathode. Tin may beselectively plated by pulse plating the non alpha particle controlledTin with current control to suppress plating of Polonium upon theplating cathode. Tin may also be selectively plated by pulse plating thenon alpha controlled Tin with potential control to suppress plating ofPolonium upon the plating cathode. Tin may also be selectively plated bypulse and reverse plating to plate out Polonium upon a filteringcathode. Tin may also be selectively plated by plating out Polonium upona filtering cathode within a concentrate. Tin may also be selectivelyplated by plating out purified Tin upon a filtering cathode, separatingthe purified Tin from the filtering cathode, and utilizing the purifiedTin to plate Tin upon the plating cathode. The isotope ²¹⁰Po emits alphaparticles at energies of 5.3 Million Electron Volt (MeV).

Referring now to the FIGs, wherein like components are labeled with likenumerals, exemplary embodiments that involve a semiconductor carrier,semiconductor device, such as a wafer, chip, integrated circuit,microdevice, etc in accordance with embodiments of the present inventionare shown, and will now be described in greater detail below. It shouldbe noted that while this description may refer to components in thesingular tense, more than one component may be depicted throughout theFIGs. The specific number of components depicted in the FIGs. and theorientation of the structural FIGs. was chosen to best illustrate thevarious embodiments described herein.

FIG. 1 depicts a semiconductor wafer 5, in accordance with variousembodiments of the present invention. Wafer 5 may include a plurality ofsemiconductor chips 10 separated by kerfs 15. Each chip 10 may includean active region 20 wherein integrated circuits including microdevicesmay be built using microfabrication process steps such as doping or ionimplantation, etching, deposition of various materials,photolithographic patterning, wire formatting, plating, etc. Wafer 5also includes an exposed area that which a plating tool electricallycontacts wafer 5 to enable plating electrically conductive materials.The wafer 5 may be diced to form individual semiconductor chips 10.

FIG. 2 depicts a cross section view of a portion of a semiconductordevice such as semiconductor wafer 5 or semiconductor chip 10, inaccordance with various embodiments of the present invention. Thesemiconductor device includes a semiconductor substrate 50 and amicrodevice 20, wiring 22, wiring contact 24 therein. The semiconductordevice also includes a contact structure including a residual platingportion 40′, plate 70, and purified solder bump 60.

The semiconductor substrate 50 may include, but is not limited to: anysemiconducting material such conventional Si-containing materials,Germanium-containing materials, GaAs, InAs and other likesemiconductors. Si-containing materials include, but are not limited to:Si, bulk Si, single crystal Si, polycrystalline Si, SiGe, amorphous Si,silicon-on-insulator substrates (SOI), SiGe-on-insulator (SGOI),annealed poly Si, and poly Si line structures. In various embodiments,substrate 50 may be, for example, a layered substrate (e.g. SOIsubstrate), a bulk substrate, a planar device substrate, etc. Thesubstrate 50 includes a microdevice 20 such as a back end of the linemicrodevice, front end of the line microdevice, middle of the linemicrodevice and wiring 22 including one or more wiring layerselectrically connected to the microdevice 20. In a particularembodiment, microdevice 20 is a field effect transistor (FET), such as afin FET, pFET, nFET, etc. The wiring 22 is electrically connected to thecontact structure by wiring contact 24. The wiring contact 24 and wiring22 allows for current to be transferred from an external surface ofsubstrate 50 to microdevice 20.

Residual plating portion 40′ is formed by retaining a portion ofshorting layer 40, shown in FIG. 4, an electrically conductive layerthat is formed upon the substrate 50 and utilized to plate electricallyconductive materials. Plate 70 is formed by plating electricallyconductive material upon the shorting layer 40 and purified solder bump60 is formed by plating solder material upon the plate 70. Purifiedsolder bump 60 is treated by various techniques as described herein toreduce alpha particle emitting elements from the solder material.

FIG. 3 depicts a cross section view of a portion of a semiconductorcarrier 100, in accordance with various embodiments of the presentinvention. The semiconductor carrier includes a laminate 102, wiring122, wiring contact 124. The semiconductor carrier 100 also includes acontact structure including a residual plating portion 140′, plate 170,and purified solder bump 60. Laminate 102 may be an organic carrier or aceramic carrier. The contact structures, wiring 124, etc. provideelectrical paths from the upper surface of carrier 100 to the opposingside of carrier 100. Residual plating portion 140′ is formed byretaining a portion of a shorting layer (not shown), formed upon thelaminate 102 and utilized to plate electrically conductive materials.Plate 170 is formed by forming a patterned photoresit upon the shortinglayer 40 and plating an electrically conductive material upon theshorting layer within the photo resist pattern. The photoresit issubsequently removed and excess shorting layer material is etched away.Purified solder bump 60 allows for the electrical connection of asemiconductor chip 10 to a particular side of laminate 102 and/or allowsfor the electrical connection of the laminate 102 to an externalelectrical device. The purified solder bump 60 may be placed, screened,etc. upon plate 170. Solder mask 120 may be formed upon the laminate 102to aid in the placement and retention of the purified solder bump 60upon plate 170. The purified solder bump 60 is treated by varioustechniques as described herein to reduce alpha emitting elements fromthe solder material.

FIG. 4 depicts a cross section view of a semiconductor device, such aswafer 5, semiconductor chip 10, etc. at a particular stage offabrication. At the present stage of fabrication, shorting layer 40 isformed upon substrate 50 and a patterned mask 80 is formed upon theshorting layer 40.

Shorting layer 40 may be formed using a sputtering technique or otherknown deposition technique. In embodiments, the shorting layer 40 maybe, for example, copper or other conductive metal such as, for example,nickel, nickel alloys, copper alloys, etc. The shorting layer 40 may bemultilayered and further include a barrier layer which may be, forexample, Titanium, Titanium Tungsten, or Titanium Tungsten Chrome. Theshorting layer 40 may be about 0.45 microns thick; although otherdimensions are also contemplated by the present invention such as, forexample, a range of about between 0.1 to 0.6 microns. In certainembodiments, shorting layer 40 is utilized as a shorting layer where aplating tool electrically contacts wafer 5 to enable plating of plate70, solder bumps, etc.

Mask 80 may be a known mask material such as a photoresist that may bepatterned formed upon the shorting layer 40. Mask 80 may be applied as aliquid upon shorting layer 40 that may dry and be patterned generallyforming trenches 82 within the mask 80 that expose portions of theshorting layer 40. For example, when mask 80 is a photoresit, a liquidphotoresist may be formed by precision spraying, roller coating, dipcoating, spin coating, etc. Exemplary liquid photoresists can be eitherpositive tone resists such as TCIR-ZR8800 PB manufactured by Tokyo OhkaKogyo America, Inc. or negative tone resists such as JSR THB 126Nmanufactured by JSR Micro, Inc., Poly(methyl methacrylate) (PMMA),Poly(methyl glutarimide) (PMGI), Phenol formaldehyde resin(DNQ/Novolac), etc. Mask 80 may also be a semi-solid film coated,laminated, or otherwise formed upon shorting layer 40. For example, mask80 may be a dry photoresist such as Asahi CX8040, Asahi CXA240, Ristonphotoresists, WBR photoresists.

Mask 80 is of sufficient thickness to form desired contact structures.As such, mask 80 may be chosen to be of a material and a thickness tosatisfy such requirements. For example, mask 80 may have a thicknessranging from about 10 um to about 500 um, although a thickness less than40 um and greater than 500 um have been contemplated. In one embodiment,mask 80 may be about 150 um to 175 um thick. Perimeter portions ofshorting layer 40 are left uncovered by mask 80 forming electricallyconductive perimeter region 42.

A pattern may be formed in the mask 80 by removing portions of the mask80. For example, when mask 80 is a photoresist, portions of the mask 80may be exposed to radiation such as deep ultraviolet light or electronbeams. Once the patterning of mask 80 is completed, portions of the mask80 may be retained and portions of mask 80 may be etched away by anetchant that removes mask 80 material. The portions of mask 80 that areetched away reveal the underlying shorting layer 40. In variousembodiments, the portions of mask 80 that are etched away form trenches82 in which electrically conductive materials may be plated within.

Referring now to FIG. 5, which depicts a plating tool 200 and wafer 5 ata stage of fabrication in which plate 70 is formed upon shorting layer40. Plating, electroplating, electrodeposition, etc. is a process inwhich wafer 5 is placed in a reservoir 210 which contains a plate 70plating solution 212 (e.g. plating bath, etc.). The wafer 5 may beattached to a fixture 220 that accepts wafer 5, wraps around wafer 5,and contacts electrically conductive perimeter region 42 such that onlythe shorting layer 40 within trenches 82 are exposed to the platingsolution 212. An electrical circuit is created when a negative terminalof a power supply contacts electrically conductive perimeter region 42of wafer 5 so as to form a cathode and a positive terminal of the powersupply is connected to plating material 214 in the tool 200 so as toform an anode.

Typically, plating tools or the power supplies themselves have thecapability of controlling pulse plating parameters. For example, in apulse plate operation, the plating tool may control the amount of timethe current is off and the amount of time the current is on which may beset upon the plating tool via a user interface. The pulse platingoperation may be controlled to a constant current or a constantpotential pulse. In the constant current mode, the tops of the currentwave form are kept flat by allowing the potential to vary during thepulse on-time. In the constant potential mode, the tops of the potentialpulses are kept flat by varying the current during the pulse on-time.Generally, pulse plating is utilized to produce fine grain flat platedmaterial. However, in embodiments described herein, pulse plating isutilized to selective plate a particular specie while suppressing theplating of another specie.

The plating material 214 may be a stabilized metal specie in the platingsolution 212. During the plating process, when an electrical current ispassed through the circuit, this metal specie is dissolved in thesolution 212 which take-up electrons forming plate 70 upon the exposedshorting layer 40 within trenches 82. In a particular embodiment, theplating material 214 may be, for example, copper (Cu). In an exemplaryCu plating process, in a sulfate solution, copper is oxidized at theanode to Cu²+ by losing two electrons. The Cu²+ associates with SO₄ ²⁻in the solution to form copper sulfate. At the cathode, the Cu²+ isreduced to metallic Cu by gaining two electrons.

Referring now to FIG. 6, which depicts a plating tool 200 and wafer 5 ata stage of fabrication in which purified solder 60 is formed upon plate70. Subsequent to the formation of plate 70, wafer 5 is placed in areservoir 210 which contains a solder 60 plating solution 213. The wafer5 may again be attached to fixture 220 that accepts wafer 5, wrapsaround wafer 5, and contacts electrically conductive perimeter region 42such that only the plate 70 within trenches 82 are exposed to theplating solution 213. An electrical circuit is created when a negativeterminal of a power supply contacts electrically conductive perimeterregion 42 of wafer 5 so as to form a cathode and a positive terminal ofthe power supply is connected to a solder 60 purified plating material216 in the tool 200 so as to form an anode. Purified plating material216 is a material upon which an alpha particle emitting reductiontechnique have been performed or a material where it has been determinedthat the alpha particle emissivity is below a predetermined acceptablethreshold.

The purified plating material 216 may be a stabilized metal specie inthe plating solution 213. During the plating process, when an electricalcurrent is passed through the circuit, this metal specie is dissolved inthe solution 213 which take-up electrons forming purified solder 60 uponthe exposed plate 70 within trenches 82. In a particular embodiment, thepurified plating material 216 may be, for example, Tin (Sn). In anexemplary Sn plating process, in a methanesulfonate solution, Sn isoxidized at the anode to Sn²+ by losing two electrons. The Sn²+associates with two CH₃SO₃ in the solution to form tin methylsulfonate.At the cathode, the Sn²+ is reduced to metallic Sn by gaining twoelectrons.

FIG. 7 depicts a cross section of a semiconductor device at particularstages of fabrication where mask 80 is removed. For example, mask 80 maybe removed chemically or by utilizing an oxygen based RIE, laser basedablative photodecomposition (APD), etc. FIG. 8 depicts a cross sectionof a semiconductor device at particular stages of fabrication whereportions of shorting layer 40 are removed and other portions 40′ of theshorting layer are retained. Portions of shorting layer 40 may beremoved by, for example, utilizing a wet etch, dry etch, or combination.In other embodiments, portions of shorting layer may be removed by otherknown processes such as, for example, liquid or gas flux techniques. Incertain embodiments only the portions of shorting layer 40 exterior thecontact structure (e.g. plate 70, etc.) are removed leaving retainedportions 40′ of the shorting layer under plate 70.

Upon the removal of portions of shorting layer 40, a contact structureis formed and may include the retained portion 40′ of shorting layer,plate 70, and solder bump 60, etc. The width/diameter of the contactstructure is generally similar to the width of the trench 82 of the mask80. In certain embodiments, an argon, oxygen, etc. RIE ash may beperformed to refresh the retained surfaces of the semiconductor devicesubsequent to the removal of mask 80 and/or removal of the portionsshorting layer 40.

It has been determined that Po is an element contributing to alphaparticle emissions, specifically the isotope ²¹⁰Po. Therefore, to reduceparticle alpha emissions, Po may be separated from Sn utilizing an alphaparticle emitting reduction technique further described herein. Byseparating Po from Sn it may be possible to utilize an inexpensive nonlow alpha particle emitting Sn and an alpha particle emitting reductiontechnique to form purified solder bumps 60.

Various alpha emitting reduction techniques are herein contemplated:

Pulse plating of a Sn and trace Po alloy anode with current control tosuppress plating of Po;

Pulse plating of a Sn and trace Po alloy anode with potential control tosuppress plating of Po;

Pulse and Reverse plating of a Sn and trace Po alloy anode with afiltering anode and filtering cathode to plate out Po upon the filteringcathode;

Plating of a Sn and trace Po concentrate with a filtering anode andfiltering cathode to plate out Po upon the filtering cathode;

Plating of a Sn and trace Po concentrate with a filtering anode andfiltering cathode to plate out Sn upon the filtering cathode andsubsequently utilizing the Sn as a plating anode;

Heating of a Sn and trace Po alloy to form and subsequently remove astannic oxide and accumulated Po concentrated within the stannic oxide;

Heating of semiconductor device comprising a Sn and trace Po solderbump(s) to form and subsequently remove a stannic oxide and accumulatedPo concentrated within the stannic oxide;

Heating of semiconductor carrier comprising a Sn and trace Po solderbump(s) to form and subsequently remove a stannic oxide and accumulatedPo concentrated within the stannic oxide, and;

Filtering Po from a plating bath utilizing a Po filter element.

FIG. 9—FIG. 17C generally depict embodiments related to platingoperations performed upon a Sn and trace Po alloy to generally reducethe concentration of Po.

FIG. 9 depicts electrochemistry Sn and Po plating curves. The x-axisplots a plating current value and the y-axis plots a plating voltagevalue. Reference to these Sn and Po plating curves may be relevant whenplating a Sn and trace Po alloy. When the Sn and trace Po alloy isplated, Sn is plated prior to the plating of Po. As depicted in the Snand Po plating curves, Sn plates (i.e. Sn²+ reduces to Sn) at a higherpotential relative to the plating (i.e., reduction of Po²+ to Po) andtherefore plates prior to Po. Thus, it is possible to selectively plateSn by controlling the potential of the plating tool to stay above theplating potential of Po.

It is also possible to selectively plate Sn by pulse plating, ensuringfast mass transport to suppress, reduce, or eliminate the plating of Po.Pulse plating involves the swift alternating of the potential or currentbetween two different values resulting in a series of pulses of equalamplitude, duration and polarity, separated by zero current. Each pulseconsists of an on-time during which potential and/or current is appliedand an off-time during which zero current is applied as. By changing thepulse amplitude and width, it is possible to change the plated materialcomposition and thickness.

In plating, the cathode is polarized negatively. This results in acharged layer of mostly positively charged ions (cations) near thesurface of the cathode. Prior to the transfer of electrons from thecathode to the cations that results in the deposition of the metal, thecations (1) adsorb onto the surface sites on the cathode and (2) thepotential at the cathode should be sufficiently negative so that anelectron transfer process can occur. Not all surface sites will transferelectrons at the same time. There are certain sites (i.e. kinks, ledges)that will enable a transfer of an electron at a lower energy barrierthan others (i.e. plateau). In addition, Sn atoms will accept anelectron at a lower potential than Po atoms. The total number ofelectrons available impacts how many total ions can deposit at any oneperiod. Each cation that is converted to metal is replenished by ionsfrom the bulk solution. In order for replenishment occur, ions must movefrom the bulk solution to the surface. The mode of this transport caneither be through diffusion or convection. Diffusion occurs within thearea of solution immediately above the surface of the cathode. Thethickness of this diffusion layer is dependent upon the agitation thatoccurs above the surface of the wafer. For example, the thickness canrange from ca. 7 to 100 um. Diffusion is slower than convection. Thus,the thinner the diffusion layer, the faster the ions can reach thesurface of the wafer.

When plating two components, there are surface potential and statisticsconcerns. If the potential is below the potential at which Po wouldplate, then only Sn would deposit. However, if the potential is suchthat both Sn and Po could plate, Sn will plate first but some Po willplate on surface sites that enable easier electron transfer to occur(i.e. a kink or ledge location). If it takes too long for the ions tomove from the bulk solution to the surface, then the ratio of Po to Snions on the surface will increase as the Sn ions are consumed.Therefore, over time more Po ions will deposit.

When direct current plating is used, a steady state situation occurs.However, the steady state is such that there is a higher ratio of Po toSn ions on the surface than the instance before the current was turnedon. With pulse plating, the anode or cathode terminal is periodicallyturned off to allow time for the ions to move across the hydrodynamicbarrier to populate the surface sites. In this manner, the ratio of Poto Sn ions is kept to a minimum which limits the amount of Po that isincorporated into the deposit. The duration of the off time pulse isdependent upon the thickness of the hydrodynamic layer. Thus, ifagitation is poor, the off time pulse must be longer to enable theadditional time for the surface sites to be repopulated before platingcommences again. The on-time is somewhat fixed in that any time longerthan a pulse of 20 msec will consume the ions on the surface sites andwill behave exactly as direct current plating. The ideal on time appearsto be between 100 microseconds and 500 microseconds. The off time isdependent upon the agitation. With maximum agitation (i.e. ca. 10 umhydrodynamic layer) the ideal off time is between 100 and 500microseconds with the off time being at least as long as the on time.Thus, pulse plating effectively increases the concentration of Sn²+ ionsat the cathode relative to the concentration of Po²+ ions at thecathode. Therefore, by pulse plating, the plating of Sn is generallyincreased while the plating of Po is generally suppressed.

FIG. 10 depicts a semiconductor device fabrication method 300 to formelectrically conductive material thereupon by selectively plating Snwhile suppressing plating of Po, according to embodiments of the presentinvention. Method 300 may be utilized in the fabrication of a wafer 5,chip 10, etc. More specifically, method 300 may be utilized in thesolder bump formation fabrication stage of the wafer 5, chip 10, etc.

Method 300 begins with associating a wafer 5 with a plating tool 200.For example, wafer 5 may be installed upon fixture 220 such that fixture220 contacts electrically conductive perimeter region 42. The wafer 5and fixture 220 assembly is inserted into the plating tool 200 and isconnected to a power supply to become a plating cathode. To plate solderbumps upon the semiconductor device, a Sn and trace Po alloy within aplating bath is electrically connected to the power supply to become aplating anode (block 302).

Method 300 may continue by selectively plating Sn while suppressingplating of Po (block 304). For example, the plating tool may plate agreater concentration of Sn than the original concentration of Sn in theSn and trace Po alloy. In other words, purified Sn having reduced alphaparticle emissions may be plated. In a particular embodiment, the Sn andtrace Po alloy anode may be pulse plated with current control toincrease the concentration of Sn plated (block 306). The term “currentcontrol” indicates that the pulse plating occurs within the plating tool200 at a particular current maintained or otherwise controlled. Forexample, the plating tool 200 may control the pulse plating currentpulse amplitude, width, etc. In a particular example, the pulse platingtechnique may utilize a 0.5 duty factor (DF). The DF indicates theproportion of plating time (e.g. 0.005 msec, etc.) to the total time. Assuch, a 0.5 DF indicates that the time of each current pulse isequivalent to the time of zero current between pulses.

FIG. 11 depicts a plating tool 200 and semiconductor device at aparticular stage of fabrication to form electrically conductive materialthereupon by selectively plating Sn while suppressing plating of Po,according to embodiments of the present invention. In the presentembodiment, plating tool 200 includes wafer 5, fixture 220, referenceelectrode 230, and a Sn and trace Po alloy 215. Wafer 5 is installed tofixture 220 such that fixture 220 contacts electrically conductiveperimeter region 42. The wafer 5 and fixture 220 assembly is insertedinto the plating tool 200 and is connected to a power supply (not shown)to become a plating cathode. To plate solder bumps upon thesemiconductor device, a Sn and trace Po alloy 215 is located withinplating bath 213 and is electrically connected to the power supply (notshown) to become the plating anode. Electrode 230 measures potential atthe plating surface of the plating bath 213. For example, the electrode230 is placed within the plating bath 213 to be coplanar with theexposed surface of plate 70 to measure the potential at exposed surfaceof plate 70. Electrode 230 allows for the plating with potential controlto increase the concentration of Sn plated. For example, electrode 230allows for plating tool to maintain or control a plating potential valueabove the plating potential of Po to suppress the plating of Po.

FIG. 12 depicts a semiconductor device fabrication method 310 to formelectrically conductive material thereupon by selectively plating Snwhile suppressing plating of Po, according to embodiments of the presentinvention. Method 310 may be utilized in the fabrication of a wafer 5,chip 10, etc. More specifically, method 310 may be utilized in thesolder bump formation fabrication stage of the wafer 5, chip 10, etc.

Method 310 begins with associating a wafer 5 with a plating tool 200.For example, wafer 5 may be installed upon fixture 220 such that fixture220 contacts electrically conductive perimeter region 42. The wafer 5and fixture 220 assembly is inserted into the plating tool 200 and isconnected to a power supply to become a plating cathode. To plate solderbumps upon the semiconductor device, a Sn and trace Po alloy 215 withinplating bath 213 is electrically connected to the power supply to becomea plating anode (block 312).

Method 310 may continue by selectively plating Sn while suppressing theplating of Po (block 314). For example, the plating tool may plate agreater concentration of Sn than the original concentration of Sn in theSn and trace Po alloy 215. In other words, purified Sn having reducedalpha particle emissions may be plated upon plate 70 forming purifiedsolder 60 from Sn and trace Po alloy 215. In a particular embodiment,the Sn and trace Po alloy 215 anode may be plated with potential controlto increase the concentration of Sn plated (block 316) to form purifiedsolder 60. The term “potential control” indicates that the potential ofthe plating solution at the surface to be plated is controlled ormaintained. For example, the plating tool 200 may control the platingpotential utilizing electrode 230 in a feedback loop to maintain theplating potential above that which Po reduces to effectively suppressthe plating of Po in the plating of purified solder 60.

FIG. 13 and FIG. 14 depict plating tools 200 and 201, respectively, anda semiconductor device at a particular stage of fabrication to formelectrically conductive material thereupon by selectively plating Snwhile suppressing plating of Po, according to embodiments of the presentinvention. The exemplary plating tools 200 and 201 generally perform apulse and reverse plate technique to selectively plate Sn upon wafer 5while suppressing the plating of Po by utilizing a filtering cathode 320and filtering anode 322 to plate Po upon the filtering cathode 320.Filtering cathode 320 and filtering anode 322 are formed from a materialthat does not dissolve in plating solution 213 and may be for example,Titanium, Niobium, etc. In a particular embodiment, the filtering anode322 has a surface area much greater relative to filtering cathode 320.For example, the filtering anode 322 has a ten times larger surface areacompared to filtering anode 320. Filtering anode 322 has a surface areamuch greater relative to filtering cathode 320 so that the anode andcathode will be reversed during the pulse reverse stages so as tocontrol the current density properly in order to concentrate Po on oneelectrode surface and then to reduce the amount of SnPo alloy dissolvedon the other. In a particular embodiment, the filtering anode 322 may bea Titanium mesh and the filtering cathode 320 may be solid Titanium.Filtering cathode 320 and filtering anode 322 are electrically connectedto a second or otherwise distinct power supply than that which isconnected to wafer 5 and Sn and trace Po alloy 215 anode.

In exemplary plating tool 200, depicted in FIG. 13, the filteringcathode 320 and filtering anode 322 are placed in reservoir 210. Thefiltering cathode 320 and filtering anode 322 are placed withinreservoir 210 to be located near each other relative to their locationaway from Sn and trace Po alloy 215. To aid in limiting electricalinterference between the first anode-cathode (i.e., Sn and trace Poalloy 215 and wafer 5) and the second anode-cathode (i.e. filteringcathode 320 and filtering anode 322), the second anode-cathode areplaced a relatively large distance away from the first anode-cathodewith neither the second anode nor second cathode placed between thefirst anode-cathode. For example, filtering cathode 320 and filteringanode 322 are placed near the bottom of reservoir 210 while Sn and tracePo alloy 215 anode is placed near wafer 5. In a particular embodiment,the filtering cathode 320 and filtering anode 322 are placed within anelectrical isolation structure 318, such as a polymer enclosure thatisolates direct solution line of site to the first anode-cathode tolimit electrical interference between the first anode-cathode and thesecond anode-cathode.

In yet another embodiment, such as that depicted in FIG. 14, thefiltering cathode 320 and filtering anode 322 are placed in a platingtool 201 filter housing in which a pump 303 circulates the platingsolution 213 within reservoir 210 across the filtering cathode 320 andfiltering anode 322. In yet another embodiment, the filtering cathode320 and/or filtering anode 322 are placed in an accessible location toallow for the replacement of the filtering cathode 320 and/or filteringanode 322.

Generally, the filtering cathode 320 and filtering anode 322 remove Poby plating out Po upon the filtering cathode 320 from Po²+ ions thataccumulate in the plating bath 213 from the plating of the Sn and tracePo alloy 215 upon wafer 5. More specifically, the first anode-cathodemay utilize known plating processes to DC plate Sn and trace Po alloy215 upon exposed plate 70 within trenches 82 at a first predetermineddeposition rate. In association with such plating processes, Sn²+ andPo²+ ions accumulate within plating solution 213. Simultaneously, thesecond anode-cathode may utilize pulse and reverse plating techniques toaccumulate Po upon the filtering cathode 320 thereby reducing the Po²+ions within the plating solution 213 and thus limiting the Po²+ ionsnear wafer 5.

During normal plating processes on the wafer 5, a vast majority (i.e.97%) of the current electrons are used to deposit Sn. The remainingcurrent electrons are used to consume hydronium ions (H⁺) to producehydrogen gas H₂. This results in an increase in Sn²+ ions into theplating solution 213. Simultaneously, Sn and trace Po alloy 215 anodewill dissolve a trace amount “x” mg Po for every gram of Sn dissolved.Note, the specific amount “x” is not critical. The trace amount “x” ofPo that is dissolved (i.e. milligrams) is much less than the amount ofSn that is dissolved (i.e. grams). If the plating is controlled, about1/10^(th) of “x” mg of Po is plated for every gram of Sn deposited. Thisresults in about 9/10^(th) “x” mg increase in plating solution 213 forevery gram of Sn plated. Over time the amount of Po deposited on thewafer 5 or another wafer 5 inserted into the plating tool wouldincrease. The filtering cathode 320 and filtering anode 322 depositsabout 20 times the Po for every gram of Sn deposited. This isaccomplished (1) having a higher current density on the filteringcathode 320 than on the wafer 5, (2) having poorer agitation on thefiltering cathode 320 that the wafer 5 cathode, (3) having longer pulseson the filtering cathode 320 to mimic DC plating and (4) locally platingpurer Sn on the filtering anode 322 during the pulse reverse stages tofurther increase the Po in the SnPo deposit on the filtering cathode320. The net reaction on the filtering cathode 320 and filtering anode322 system will be to generate hydronium ions at the filtering anode 322and deposit SnPo alloy at the filtering cathode 320. The total mass willbe about 3% of that deposited on the wafer 5 cathode. This results inconsuming the extra Sn²+ accumulated in the plating solution 213 andadding back the hydronium ions consumed on the wafer 5 cathode. In thisway, the total dissolved Po+ in plating solution 213 is maintainedconstant if using a Sn and trace Po alloy 215. If using a purified Sn214 anode, then the overall Po²+ in solution would decrease. Thus, thefiltering cathode 320 and filtering anode 322 will maintain or improvethe plating solution 213 resulting in a lower alpha particle count onthe wafer 5 associated with the formation of purified solder bumps 60.

In pulse and reverse plating, a cathodic pulse is followed by an anodicpulse. The terms cathodic and anodic are utilized to described thecurrent direction in that cathodic indicates that current flow is innormal plating direction (from cathode to anode) and anodic indicatesthat current flow is in reverse or deplating direction (from anode tocathode). Thus, cathodic and anodic pulses are applied to filteringcathode 320 and filtering anode 322, respectively, to produce a depositon the filtering cathode that is about 20 times greater in concentrationthan what is deposited on the wafer cathode. This results in maintainingor reducing the Po⁺ concentration in solution.

In a particular embodiment, the Po is plated upon the filtering cathode320 at a second higher deposition rate relative to the predeterminedfirst deposition rate of Sn upon wafer 5. For example, with cathodicpulses, the Po is plated upon the filtering cathode 320 at approximatelytwice the deposition rate of Sn plating upon wafer 5 and, with anodicpulses, is deplated from the filtering cathode 320 at approximately⅛^(th) the rate of Sn plating upon wafer 5. Thus, over time, Poaccumulates upon the filtering cathode 320 thereby reducing the Po²+ions within the plating solution 213. In another embodiment, the anodicpulses and cathodic pulses may last at least 20 msec. and may beseparated by a non plating time of at least 20 msec.

FIG. 15, FIG. 16A, and FIG. 16B depict respective tanks 400, 402, 402utilized to separate Po from Sn and trace Po alloy 215, according toembodiments of the present invention. Tanks 400, 402 may be utilized bya plating bath vendor to fabricate purified Sn, purified Sn concentrate,etc. from the Sn and trace Po alloy 215. As shown in FIG. 15, a Snconcentrate 410 is formed from the Sn and trace Po alloy 215 in a firsttank 400. For clarity, because Sn concentrate 410 was formed from Sn andtrace Po alloy 215, Sn concentrate 410 includes both Sn²+ ions and Po²+ions. In a particular embodiment, the Sn concentrate may be formed bydissolving Sn and trace Po alloy 215 using an acid. The Sn concentrate410 is then moved into a second tank 402.

As shown in FIG. 16A, the second tank 402 may also include filteringcathode 320 and filtering anode 322 to reduce the concentration of Po²+ions within the Sn concentrate 410 by plating out Po 404 upon thefiltering cathode 320. The purified Sn concentrate 410 having reducedPo²+ ions may then be utilized in a Sn plating process to plate a testsample of Sn material. The test sample of plated Sn material may betested to determine whether the Sn material meets a predeterminedmaximum alpha particle emitting threshold. For example, the sampleplated Sn material may be tested to see whether it has an alpha particleemitting value of less than 2α/cm²/1000 hours. If the sample plated Snmaterial does not meet the predetermined alpha emitting threshold, theplated Sn material is utilized to form another Sn concentrate 410 in afirst tank that is subsequently purified by plating out Po upon thefiltering cathode 320 in a second tank. This process may be iterativelyperformed until the plated Sn material meets the predetermined alphaparticle emitting threshold.

As shown in FIG. 16B, the second tank may also include filtering cathode420 and filtering anode 422 to filter the Sn concentrate 410 by platingout Sn upon the filtering cathode 420. The filtering cathode 420 has asurface area that is as least 10 times that of the filtering anode 422.In a particular embodiment, the filtering cathode 420 is formed from amaterial in which Sn that is plated thereto and may be separated therefrom. The filtering anode 422 may be either the Sn with trace Po alloy,a purified Sn metal, or an insoluble anode such as platinum, titanium orniobium. A downside of using an insoluble anode in this configuration isthat the acid concentration will continue to increase and once the acidconcentration goes above a value that destabilizes the bath (ca. 350 to400 g/L methylsulfonic acid), the solution would need to be removed. Thetank 402 in FIG. 16B may also include a membrane, such as Nafion,between the filtering anode 422 to filter the Sn concentrate 410 toreduce the increasing acid concentration issue when using an insolubleanode. The liquid in the side of the tank 403 nearest the anode which iscalled the anolyte will be filled with a low concentration ofmethylsulfonic acid. In this way, the acid can increase within theanolyte without impacting the quality of the concentrate that is beingpurified. Therefore, either the concentrate solution 410 can be extendedto plate out as much purified Sn as possible, or a continuous feed stockof solution 410 can be added to create a continuous batch operationconfiguration.

The filtering cathode 420 and filtering anode 422 are electricallyconnected to a power supply (not shown) and may implement currentcontrolled or potential controlled pulse plating to selectively platepurified Sn 405 upon the filtering cathode 420. For example, a currentcontrolled pulse plating technique mimics an increase of agitation ofthe Sn concentrate 410 to increase the concentration of Sn²+ ions nearfiltering cathode 420. In another example, a potential controlled pulseplating technique limits the plating potential to be below the platingpotential of Po. If the potential controlled pulse plating technique isutilized a reference electrode is added to tank 402 to measure thepotential at the plating surface of filtering cathode 420, similar tothe reference electrode 230 depicted in FIG. 11. In a particularembodiment, a particular plating technique results in high plating bathagitation at the surface of filtering cathode 420 and includes adeposition pulse on-time of less than 10 msec with and a 0.5 DF.

Subsequent to plating purified Sn 405 upon the filtering cathode 420,the plated purified Sn 405 is separated from the filtering cathode 420.For example, the plated Sn is separated from the filtering cathode 420by dissolving the purified Sn 405 electrolytically and collecting thepurified Sn 405 using a membrane. The separated purified Sn 405 may thenbe utilized in a plating bath to plate a test sample of the purified Sn405 be tested to determine whether the purified Sn 405 material meets apredetermined maximum alpha particle emitting threshold. For example,the sample plated purified Sn 405 may be tested to see whether it has analpha particle emitting value of less than 2α/cm²/1000 hours. If thesample plated purified Sn 405 does not meet the predetermined alphaparticle emitting threshold, the plated purified Sn 405 is utilized toform another Sn concentrate 410 that is subsequently purified byselectively accumulating further purified Sn 405 upon the filteringcathode 420 while suppressing the plating of Po upon the filteringcathode 420. This process may be iteratively performed until the platedpurified Sn 405 material meets the predetermined alpha particle emittingthreshold.

FIG. 17A depicts a method 450 to separate Po from Sn and trace Po alloy215, according to embodiments of the present invention. Method 450 maybe utilized, for example, when plating purified solder bumps 60 upon asemiconductor device. Method 450 begins by utilizing Sn and trace Poalloy 215 as a plating anode (block 452). Sn and trace Po alloy 215 isassociated with a plating cathode, such as wafer 5. Both Sn and trace Poalloy 215 and the plating cathode are electrically connected to a firstpower supply. A plating technique, such as DC plating, pulse plating,etc. may be utilized to plate Sn and trace Po alloy 215 upon the platingcathode at a predetermined first deposition rate.

Method 450 may continue utilizing a filtering cathode 320 and filteringanode 322 simultaneously with the Sn and trace Po alloy 215 anode andplating cathode (block 454). The filtering cathode 320 and filteringanode 322 are electrically connected to a second power supply. Method450 may continue by selectively plating Sn upon the plating cathode andsuppressing the plating of Po upon the plating cathode (block 456). Forexample, a pulse and reverse plating technique is utilized (block 458)with the filtering cathode 320 and filtering anode 322 to accumulate Poupon the filtering cathode 320 (block 460). By accumulating Po upon thefiltering cathode 320, Po²+ ions are reduced within plating solution 213thereby increasing the Sn²+ ions near the plating cathode. In this way,a relatively greater concentration of Sn²+ ions are located near wafer 5thus increasing the concentration of Sn plated upon wafer 5 to formpurified solder bumps 60. In a particular embodiment, the Po is platedupon the filtering cathode 320 at a second higher deposition raterelative to the predetermined first deposition rate. For example, withcathodic pulses, the Po is plated upon the filtering cathode 320 atapproximately twice the deposition rate of Sn plating upon wafer 5 andwith anodic pulses, is deplated from the filtering cathode 320 atapproximately ⅛^(th) the rate of Sn plating upon wafer 5. Thus, overtime, Po accumulates upon the filtering cathode 320 thereby reducing thePo²+ ions within the plating solution 213 and allowing for the selectiveplating of Sn upon the plating cathode and the suppression of plating Poupon the plating cathode.

FIG. 17B depicts a method 462 to separate Po from Sn and trace Po alloy215, according to embodiments of the present invention. Method 462 maybe utilized by a plating bath vendor to provide purified platingproducts formed from Sn and trace Po alloy 215. Method 462 may begin bycreating a Sn and trace Po concentrate 410 from Sn and trace Po alloy215 (block 464). For example, Sn and trace Po alloy 215 may be dissolvedin acid and oxidized utilizing a electrolytic membrane processes. The Snand trace Po concentrate 410 may be formed in a first tank 400.

Method 462 may continue by utilizing a filtering cathode 320 andfiltering anode 322 to plate out Po of the Sn and trace Po concentrate410 upon the filtering cathode 320 (block 466). The Sn and trace Poconcentrate 410 may be transferred to a second tank 402 that furtherincludes the filtering cathode 320, filtering anode 322, and a powersupply electrically connected to the filtering cathode 320 and filteringanode 322.

Method 462 may continue by utilizing a pulse and reverse platingtechnique (block 470) with the filtering cathode 320 and filtering anode322 to accumulate Po upon the filtering cathode 320 (block 472). Byaccumulating Po upon the filtering cathode 320, Po²+ ions are reducedwithin Sn and trace Po concentrate 410. This purified Sn and trace Poconcentrate 410 is then utilized in a plating tool to plate a purifiedSn sample (block 474). The test sample of plated Sn material may betested to determine whether the Sn material meets a predeterminedmaximum alpha particle emitting threshold (block 476). For example, thesample plated Sn material may be tested to see whether it has an alphaparticle emitting value of less than 2α/cm²/1000 hours. If the sampleplated Sn material does not meet the predetermined alpha particleemitting threshold, the plated Sn material is utilized to form anotherSn concentrate 410 (block 480) and method 462 returns to block 466. Ifthe sample plated Sn material does meet the predetermined alpha emittingthreshold, the purified Sn and trace Po concentrate 410 is marked as lowalpha emitting and method 462 ends at block 478. In some embodiments,the purified Sn and trace Po concentrate 410 may be sold to a customeras a low alpha particle emitting plating bath, as a low alpha particleemitting Sn formed from the purified Sn and trace Po concentrate 410,etc.

FIG. 17C depict a method 484 to separate Po from Sn and trace Po alloy215, according to embodiments of the present invention. Method 484 maybe utilized by a plating bath vendor to provide purified platingproducts formed from Sn and trace Po alloy 215. Method 484 may begin bycreating a Sn and trace Po concentrate 410 from Sn and trace Po alloy215 (block 486). For example, Sn and trace Po alloy 215 may be dissolvedin acid and oxidized utilizing an electrolytic membrane processes. TheSn and trace Po concentrate 410 may be formed in a first tank 400.

Method 484 may continue by utilizing a filtering cathode 420 andfiltering anode 422 (block 488) to plate out purified Sn 405 from the Snand trace Po concentrate 410 upon the filtering cathode 420 (block 490).The Sn and trace Po concentrate 410 may be transferred to a second tank402 that further includes the filtering cathode 420, filtering anode422, and a power supply electrically connected to the filtering cathode420 and filtering anode 422. The filtering cathode 420 and filteringanode 422 may be associated with a current controlled or potentialcontrolled pulse plating technique to selectively plate purified Sn 405upon the filtering cathode 420. For example, a current controlled pulseplating technique increases agitation of the Sn concentrate 410 toincrease the concentration of Sn²+ ions near filtering cathode 420. Inanother example, a potential controlled pulse plating technique limitsthe plating potential to be below the plating potential of Po. If thepotential controlled pulse plating technique is utilized, a referenceelectrode is added to the plating system to measure the potential at theplating surface of filtering cathode 420. The potential of the referenceelectrode may be utilized in a feed back loop by the plating system tocontrol the system's plating potential.

Subsequent to plating purified Sn 405 upon the filtering cathode 420,the plated purified Sn 405 is separated from the filtering cathode 420(block 494). For example, the plated Sn is separated from the filteringcathode 420 by dissolving the purified Sn 405 electrolytically andcollecting the purified Sn 405 using a membrane. The separated purifiedSn 405 may then be utilized in a plating system to plate a test sampleof the purified Sn 405 (block 498). The plated purified Sn 405 may betested to determine whether the purified Sn 405 material meets apredetermined maximum alpha particle emitting threshold (block 500). Forexample, the sample plated purified Sn 405 may be tested to see whetherit has an alpha particle emitting value of less than 2α/cm²/1000 hours.If the sample plated purified Sn 405 does not meet the predeterminedalpha emitting threshold, the plated purified Sn 405 is utilized to formanother Sn concentrate 410 that is subsequently purified by selectivelyaccumulating further purified Sn 405 upon the filtering cathode 420while suppressing the plating of Po upon the filtering cathode 420(block 502). If the sample plated purified Sn 405 does meet thepredetermined alpha particle emitting threshold, the plated purified Sn405 is marked as low alpha particle emitting and method 484 ends atblock 504. In some embodiments, the purified Sn 405 or concentratedformed from the purified Sn 405 may be sold to a customer as a low alphaparticle emitting plating product.

FIG. 18-FIG. 22 generally depict embodiments related to the heating Snand trace Po alloy 215 to form and subsequently remove a stannic oxideand accumulated Po concentrated within the stannic oxide.

Referring to FIG. 18, Sn and trace Po alloy 215 is depicted as a rawalloy. In some embodiments, the Sn and trace Po alloy 215 may be a standalone element. In other embodiments, the Sn and trace Po alloy 215 maytake the form of plated solder upon a wafer 5, plated solder upon asemiconductor chip 10. In still other embodiments, the Sn and trace Poalloy 215 may take the form of solder placed upon laminate 100.

FIG. 19A depicts a Sn and trace Po alloy 215, Sn oxidation and Poheating operation 420, according to embodiments of the presentinvention. Heating operation 520 generally heats the Sn and trace Poalloy 215 in air to a temperature to form Sn oxide 524 but below themelting point of Sn and trace Po alloy 215. Heating operation 520generally forms Sn oxide 524 upon exposed perimeter of Sn and trace Poalloy 215. The oxidation of Sn process results in Po 526 gettering tothe Sn oxide 524. As a result of the Po 526 gettering to the Sn oxide524, the inner portion of Sn and trace Po alloy 215 consists of a higherconcentration of Sn relative to the concentration of Sn in Sn and tracePo alloy 215. This increased Sn portion of the inner Sn and trace Poalloy 215 is referred to as purified Sn 522.

FIG. 19B depicts the Sn and trace Po alloy 215 Sn oxidation and Poheating operation 520 performed upon a semiconductor device, such aswafer 5, semiconductor chip 10, etc. according to embodiments of thepresent invention. In the present embodiment, Sn and trace Po alloy 215may take the form of plated solder bumps upon the semiconductor device.It may be previously determined that the semiconductor device has analpha particle emission rate above a predetermined threshold. As opposedto scrapping the semiconductor device, it may undergo the Po heatingoperation 420 to accumulate the gettered Po 526 within the exposedoxidized Sn perimeter 524. The semiconductor device may undergosubsequent operations, described below, to remove the Sn oxide 524 andgettered Po, thus reducing alpha emitting particles that at leastpartially gave rise to the semiconductor device having the alphaparticle emission rate above the predetermined threshold.

FIG. 19C depicts the Sn and trace Po alloy 215 Sn oxidation and Poheating operation 420 performed upon a semiconductor carrier 100,according to embodiments of the present invention. In the presentembodiment, Sn and trace Po alloy 215 may take the form of placed solderbumps upon the carrier 100. It may be previously determined that thesemiconductor carrier 100 has an alpha particle emission rate above apredetermined threshold. As opposed to scrapping the semiconductorcarrier 100, it may undergo the Po heating operation 520 to accumulatethe gettered Po 526 within the exposed oxidized Sn perimeter 524. Thesemiconductor carrier 100 may undergo subsequent operations, describedbelow, to remove the Sn oxide 524 and gettered Po, thus reducing alphaemitting particles that at least partially gave rise to thesemiconductor carrier 100 having the alpha particle emission rate abovethe predetermined threshold.

FIG. 20 depicts purified Sn 522 that includes Sn and reduced Po,relative to Sn and trace Po alloy 215, according to embodiments of thepresent invention. Subsequent to forming Sn oxide 524 and gettering Po526 within the Sn oxide 524, the accumulated Po 526 may be removed bystripping off the Sn oxide 524 leaving the purified Sn 522. The purifiedSn 522 may be tested for alpha particle emissions to determine if itsalpha particle emission rate meets a predetermined threshold. If so, thepurified Sn 522 may be utilized in plating operations. For example, thepurified Sn 522 may be used as the purified plating material 216, asshown in FIG. 6 to plate purified solder bumps 60 upon wafer 5.

In embodiments where the oxidized Sn 524 and trace Po alloy 215 isutilized as a solder and is located upon a semiconductor device or asemiconductor carrier 100, the Sn oxide 524 may be removed by applying asolder flux to the solder, performing a solder reflow to dissolve the Snoxide 524 and Po 526 in the flux, and performing a flux clean to removethe flux, the Sn oxide 524, and the Po 526. The semiconductor device orsemiconductor carrier 100 may be again tested to determine whether itsalpha particle emission rate meets the threshold. If not, thesemiconductor device or semiconductor carrier 100 may again be putthrough heating operation 520 where additional Po 526 is accumulated inSn oxide 524 and subsequently removed.

FIG. 21 depicts a method 530 of forming purified Sn 522 including Sn andreduced Po 526, relative to an initial concentration of Po, according toembodiments of the present invention. Method 530 may be utilized tocreate raw material, such as purified plating material 216 Sn that is alow alpha particle emission material from Sn and trace Po alloy 215 thatis not a low alpha particle emission material. Method 530 begins byaccumulating Po 526 within the Sn and trace Po alloy 215 (block 532).For example, Sn and trace Po alloy 215 may be heated in air to atemperature to form Sn oxide 524 upon the perimeter but less than themelting point of the Sn and trace Po alloy 215 (block 532). The heatingof Sn and trace Po alloy 215 oxidizes Sn at exposed perimeter surfacesof the Sn and trace Po alloy 215 (block 536). The Sn oxidizationprocesses getters Po 526 to the Sn oxide 524 (block 538). In otherwords, the Po 526 becomes concentrated within the Sn oxide 524.

Method 530 may continue by removing the Sn oxide 524 forming purified Sn522 including Sn and reduced Po 526 (block 540). The Sn oxide 524 may beremoved by known techniques. Along with the Sn oxide 524, theaccumulated Po 526 is also removed. Thus the relative concentration ofSn in the remaining material is increased and forms purified Sn 522. Forclarity, purified Sn 522 may still include a trace amount of Po 526 butthe relative concentration of Po is reduced compared to the initialconcentration of Po 525 in Sn and trace Po alloy 215. Method 530 maycontinue by testing the purified Sn 522 for alpha particle emissions todetermine if its alpha particle emission rate meets a predeterminedthreshold. If so, method 530 ends at block 536 and the purified Sn 522may be subsequently utilized in plating operations e.g., as purifiedplating material 216 in order to plate purified solder bumps 60. If thepurified Sn 522 does not meet the alpha particle emission threshold themethod 530 returns to block 532 where the purified Sn 522 is operatedupon to accumulate and remove Po 526.

FIG. 22 depicts a method 550 of forming a purified Sn 522 solder bump,including Sn and reduced Po 526 solder bump, upon a semiconductordevice, such as wafer 5, semiconductor chip 10, or semiconductor carrier100, according to embodiments of the present invention. Method 550 maybe utilized to rework a fabricated wafer 5, semiconductor chip 10, orsemiconductor carrier 100 that does not meet an alpha particle emissionthreshold to reduce the alpha particle emissions thereof. Method 550begins by accumulating Po 526 within Sn and trace Po alloy 215 solderbump (block 552). Generally the solder bump may be plated upon, placedupon, etc. the fabricated wafer 5, semiconductor chip 10, orsemiconductor carrier 100. The Po 526 may be accumulated by heating thefabricated wafer 5, semiconductor chip 10, or semiconductor carrier 100in air to a temperature to form Sn oxide 524 upon the perimeter of thesolder bump but less than the melting point of the solder bump (block554). The heating of the solder bump oxidizes Sn 524 at exposedperimeter surfaces of the Sn and trace Po alloy 215 solder bump (block556). The Sn oxidization processes getters Po 526 to the Sn oxide 524(block 538). In other words, the Po 526 becomes concentrated within theSn oxide 524.

Method 550 may continue by removing the Sn oxide 524 forming purified Sn522 including Sn and reduced Po 526 (block 560). The Sn oxide 524 may beremoved by applying flux the solder bump (block 562), performing asolder reflow to activate the flux and dissolve the Sn oxide 524 and Po526 in the flux (block 564), and performing a flux clean to remove theflux, the Sn oxide 524, and the Po 526 (block 566). Thus the relativeconcentration of Sn in the remaining solder bump is increased. Forclarity, the remaining solder bump may still include a trace amount ofPo 526 but the relative concentration of Po is reduced compared to theinitial concentration of Po 525 in the Sn and trace Po alloy 215 solderbump. Method 550 may continue by testing the fabricated wafer 5,semiconductor chip 10, or semiconductor carrier 100 for alpha particleemissions to determine if its alpha particle emission rate meets thepredetermined threshold. If so, method 550 ends. If the fabricated wafer5, semiconductor chip 10, or semiconductor carrier 100 does not meet thealpha particle emission threshold method 550 returns to block 552 wherethe fabricated wafer 5, semiconductor chip 10, or semiconductor carrier100 is operated upon to further purify the solder bump.

FIG. 23-FIG. 27 generally depict embodiments of filtering Po from aplating bath utilizing a Po filter element.

FIG. 23 depicts a plating tool 200 and semiconductor wafer 5 at aparticular stage of fabrication in which purified solder 60 is formedupon plate 70. Subsequent to the formation of plate 70 the wafer 5 isplaced in a reservoir 210 which contains a solder 60 plating solution213, such as SnAg plating bath. The wafer 5 may again be attached tofixture 220 that accepts wafer 5, wraps around wafer 5, and contactselectrically conductive perimeter region 42 such that only the plate 70within trenches 82 are exposed to the plating solution 213. Anelectrical circuit is created when a negative terminal of a power supplycontacts electrically conductive perimeter region 42 of wafer 5 so as toform a cathode and a positive terminal of the power supply is connectedto a Sn and trace Po alloy 215 in the tool 200 so as to form an anode.

The Sn and trace Po alloy 215 may be a stabilized metal specie in theplating solution 213. During the plating process, when an electricalcurrent is passed through the circuit, the Sn and trace Po alloy 215 isdissolved resulting in Sn²+ ions and Po²+ ions in the solution 213. ThePo²+ ions in the solution 213 are filtered from the solution 213 by Pofiltering element 800. In the embodiment depicted in FIG. 23, the Pofiltering element 800 is placed in a plating tool 200 filter housing inwhich a pump 303 circulates the plating solution 213 within reservoir210 across the Po filtering element 800. In yet another embodiment,depicted in FIG. 27, the Po filtering element 800 is placed in anaccessible location, for example in base of the reservoir 210, to allowfor the replacement of the Po filtering element 800. Generally, the Pofiltering element 800 reduces Po²+ ions in the solution 213 by the Po²+ions take-up electrons from the Po filtering element 800 therebyabsorbing Po within the Po filtering element 800. By reducing the Po²+ions in the solution 213 a greater concentration of Sn²+ ions aremaintained in the solution 213 to plate upon wafer 5.

FIG. 24 depicts a Po filter element 800, in accordance with variousembodiments of the present invention. Po filter element 800 has highsurface area and can be made from Titanium, such as a mesh, comprisingan outer stannic oxide perimeter. The Po filter element 800 may beformed by immersing the high surface area Titanium into a solution ofSn(II) MSA. The Sn(II) reduces onto the high surface area Titanium aspure Sn and corrodes Ti(II) into the Sn(II) MSA solution. Upon removalfrom the Sn(II) MSA solution, the high surface area Titanium includes apure Sn perimeter. The high surface area Titanium which includes thepure Sn perimeter may be subsequently heated to oxidize the Sn perimeterconverting the pure Sn to stannic oxide forming Po filter element 800.For example, in a particular embodiment, the high surface area Titaniumwhich includes the pure Sn perimeter may he heated in air at 150 degreesCelsius for 2 hours to convert the pure Sn to stannic oxide. Po filterelement 800 may then be placed within the plating tool to allow thestannic oxide perimeter to getter Po²+ ions in the solution 213 by thePo²+ ions adsorbing and entering within the stannic oxide perimetercausing Po to be sequestered within the Po filter element 800. Over timePo filter element 800 may loose available absorption sites to sequesterPo within the Po filter element 800. As such, the Po filter element 800may be occasionally replaced with a new Po filter element 800. In oneembodiment, the Po filter element 800 can be removed, rinsed, dried andthe alpha particle emission measured to see if the filter is saturatedwith Po.

FIG. 25 depicts a method 802 of forming a Po filter element 800, inaccordance with various embodiments of the present invention. Method 802begins with reducing pure Sn upon a high surface area Titanium, such asa Titanium mesh (block 804). For example, the high surface area Titaniummay be immersed in a solution of Sn(II) MSA. The Sn(II) reduces onto thehigh surface area Titanium as pure Sn and corrodes Ti(II) into theSn(II) MSA solution. Upon removal from the Sn(II) MSA solution, the highsurface area Titanium comprises pure Sn perimeter.

Method 802 continues by converting the pure Sn to a stannic oxideperimeter (block 806). For example, the high surface area Titanium whichincludes the pure Sn perimeter may be heated to oxidize the pure Snperimeter converting the pure Sn to stannic oxide. In a particularimplementation, the Titanium mesh which includes the pure Sn perimetermay he heated in air at 150 degrees Celsius for 2 hours to convert thepure Sn perimeter to a stannic oxide perimeter.

FIG. 26 depicts a method 810 of filtering Po from a plating bath 213, inaccordance with various embodiments of the present invention. Method 810may be utilized, for example, by a semiconductor device fabricator.Method 810 begins at block 812 and continues with filtering Po, Po ions,etc. from plating bath 213 (block 814). During plating, when anelectrical current is passed through the plating anode and platingcathode, the Sn and trace Po alloy 215 anode is dissolved resulting inSn²+ ions and Po²+ ions in the solution 213. The Po²+ ions in thesolution 213 are filtered from the solution 213 by Po filtering element800. In an embodiment, the Po filtering element 800 is placed in aplating tool 200 filter housing in which a pump 303 circulates theplating solution 213 within reservoir 210 across the Po filteringelement 800 (block 816). In yet another embodiment, the Po filteringelement 800 is placed in an accessible location, for example in base ofthe reservoir 210, to allow for the replacement of the Po filteringelement 800 (block 816). Method 810 may continue by the Po filteringelement 800 reducing Po²+ ions in the solution 213 by the Po²+ ionstaking-up electrons from the Po filtering element 800 thereby plating Poupon the Po filtering element 800. (block 818). By reducing the Po²+ions in the solution 213 a greater concentration of Sn²+ ions aremaintained in the solution 213 to plate upon the semiconductor device.Method 810 ends at block 820.

The accompanying figures and this description depicted and describedembodiments of the present invention, and features and componentsthereof. Those skilled in the art will appreciate that any particularnomenclature used in this description was merely for convenience, andthus the invention should not be limited by the specific processidentified and/or implied by such nomenclature. Therefore, it is desiredthat the embodiments described herein be considered in all respects asillustrative, not restrictive, and that reference be made to theappended claims for determining the scope of the invention.

The exemplary methods and techniques described herein may be used in thefabrication of integrated circuit chips. The resulting integratedcircuit chips can be distributed by the fabricator in raw wafer form(i.e., as a single wafer that has multiple unpackaged chips), as a baredie, or in a packaged form. In the latter case, the chip is mounted in asingle chip package (e.g., a plastic carrier, with leads that areaffixed to a motherboard or other higher level carrier) or in amultichip package (e.g., a ceramic carrier that has either or bothsurface interconnections or buried interconnections). The chip is thenintegrated with other chips, discrete circuit elements and/or othersignal processing devices as part of either (a) an intermediate product,such as a motherboard, or (b) an end product. The end product can be anyproduct that includes integrated circuit chips, ranging from toys andother low-end applications to advanced computer products having numerouscomponents, such as a display, a keyboard or other input device and/or acentral processor, as non-limiting examples.

What is claimed is:
 1. A method of fabricating a filter comprising a Polonium (Po) filter element that filters Po, the method comprising: forming a Tin (Sn) exterior upon a Titanium (Ti) interior, and; converting the Sn exterior to a stannic oxide exterior.
 2. The method of claim 1, wherein forming Sn upon the Ti interior further comprises: immersing the Ti interior in a Tin(II) Methane Sulfonate solution.
 3. The method of claim 2, wherein pure Sn reduces onto the Ti interior and Ti(II) is corroded into the Tin(II) Methane Sulfonate solution.
 4. The method of claim 1, wherein converting the Sn to stannic oxide further comprises: heating the Sn exterior in air at a temperature below the melting point of Sn to oxidize the Sn to stannic oxide.
 5. The method of claim 1, wherein converting the Sn to stannic oxide comprises: heating the Sn exterior in air at 150° C. 